Numerous types of feeder are employed in order to transport or move people and/or objects, for example, belt conveyor feeder, screw-type feeder, cylinder-type feeder, timing belt-type feeder, lift-type feeder, industrial robots, and the like. Feeder of other types that can substitute for these feeder are disclosed in Patent Documents 1 to 5.
The feeders disclosed in Patent Documents 1 to 5 are of a design in which a moving body undergoes reciprocating motion as reeling apparatus alternately reels and unreels linear bodies connected to the moving body. In these documents, Patent Documents 1 and 2 are indicated to satisfy requirements as to positioning accuracy, long-distance transportation, remote transportation, controllability, high feed accuracy, high-speed feeding, low price, simplicity of configuration, space saving design, reduced weight, countermeasures against dust, safety measures against accidents, and the like. These feeder have additional desirable effects in terms of higher accuracy and improved durability, based on quieter and more stable operational status; more compact configuration; and higher accuracy and improved durability, based on proper reeling and unreeling of the linear bodies. The techniques disclosed in these documents are expected to contribute in the field of industrial robots and other technical fields.
In the feeder mentioned above, in cases in which it is desired to better ensure positioning accuracy controllability, high feed accuracy, and so on, the issue of extension of the linear bodies must be rigorously dealt with. Extension of linear bodies includes the widely-known types of “initial extension” and “elastic extension.” Hereinbelow, after explaining the subject of this type of extension in linear bodies, relevant issues will be discussed.
“Initial extension” ordinarily occurs in an initial stage of use of a linear body (for example, a brand-new wire rope). The cause of this is thought to be due to the fact that the helical element wires or strands of such a brand-new linear body are not yet in a state of sufficiently close contact with one another. When a load is applied on a brand-new linear body, the element wires or strands contact with one another (a tightened state), initial extension commensurate with the tensing occurs. This initial extension is also termed “permanent extension,” since the extension does not return to its original state even when unloaded. Due to the nature of initial extension, wire ropes composed of a large number of element wires, or fiber core wire ropes, tend to have greater initial extension. The extent of initial extension of linear bodies varies depending on the structure of the linear body as well. Consequently, initial extension of a linear body is also known as “structural extension.” Initial extension typically arises in a low-load range of about 10-15% of a breaking load of the linear body. However, such extension can be reduced by several tens of percent by providing the linear body with tensile processing in the final stage of a twisting operation. However, in terms of processing technique, process duration, process cost, and the like, it is difficult to eliminate in advance 100% of the initial extension in brand-new linear bodies prior to actual use.
When a tensile load is applied on a linear body from which initial extension has been eliminated, elongation proportional to the load arises in the linear body. This is well-known elastic extension which satisfies Hooke's law. This elastic extension represents “transient extension” that substantially disappears when tensile load is no longer applied.
In some instances, the aforedescribed initial extension (permanent extension) and elastic extension of linear bodies may be ignored, depending on the intended use of the feeder. Also, the allowable range of the initial extension is broadened under the conditions in which the feeder will be used. On the other hand, in the case of an accurate feeder in which it is necessary for the moving body to be halted precisely at a predetermined location on a production line or assembly line, it is important to eliminate the influence from the initial extension and elastic extension as much as possible, and if this is not accomplished to a sufficient extent, feed accuracy is considerably diminished. As a countermeasure, the linear body may be shortened each time that the initial extension exceeds a certain value. However, this practice involves performing numerous steps, such as measurement, cutting, reconnection, and the like, on the linear body while installed in the apparatus, which makes it undesirable for practical purposes.
Patent Document 6 discloses means for correcting feed error caused by “elongation of the linear bodies” in a linear body-type feeder can be corrected. The technique disclosed in this document is desirable in terms of satisfying requirements such as controllability for the purposes of error correction, stability of the state of error correction, reliability of the state of error correction, safety of the system, ease of operation, demand responsiveness, space saving design, simplicity of configuration, ease of repair and inspection, low price, low running costs, establishment of automation, assurance of high feed accuracy with respect to the feed means, and so on.